1. Field of the Invention
The present invention relates to an optical device, an optical tunable filter, an optical tunable filter module, and an optical spectrum analyzer.
2. Description of the Related Art
For example, an optical tunable filter for separating only light having a specific wavelength from light having a plurality of wavelengths has been known as an optical device. For instance, U.S. Pat. No. 6,747,775 (Patent Document 1) discloses such an optical tunable filter.
An optical tunable filter disclosed by Patent Document 1 has a movable portion in the form of a plate, support substrates, and reflection films formed on opposed surfaces of the movable portion and the support substrate, respectively. The movable portion is movable in a thickness direction thereof. One of the reflection films is formed on a surface of the movable portion near the support substrate, and the other of the reflection films is formed on a surface of the support substrate near the movable portion.
Further, drive electrodes are provided on the support substrate. When a potential difference is generated between the drive electrodes and the movable portion, an electrostatic attraction force is generated between the drive electrodes and the movable portion so as to move the movable portion. Thus, a clearance between two reflection films can be adjusted by moving the movable portion. When light having a plurality of wavelengths is introduced into the clearance, an interference effect is caused so as to emit only light having a wavelength corresponding to the clearance.
However, the drive electrodes of the optical tunable filter of Patent Document 1 face only one surface of the movable portion. Accordingly, a driving force is applied to the movable portion only in one direction. Thus, in order to increase the amount of movement of the movable portion, a large driving voltage is required. Further, if the amount of movement of the movable portion is increased only in one direction, then an excessive stress may be produced in the movable portion, so that the movable portion is damaged. Therefore, it is difficult to widen a movable range of the movable portion. It is also difficult to widen a configurable range of the clearance for interference of light. As a result, a range of available wavelengths is narrow.